1. Field Of The Invention
The present invention relates to personal communication networks; and more particularly, to a method and system of effecting hand over between personal communication networks.
2. Description Of Related Art
Heretofore, there has been made available certain frequency bands of the electromagnetic spectrum for personal Communications Service networks (PCS). PCS service providers (PSPs) will use these frequency bands to provide radio communications to mobile radio terminals (e.g. portable telephones) in limited geographic areas.
Some PSPs may want to utilize the switching and/or database infrastructure owned and operated by Local Exchange Carriers (LECs), which are companies that provide local telephone service, in some of their market for more efficient use of the PSPs' resources.
There are a number of different proposed PCS technologies. These different PCS technologies use different techniques for communicating with the mobile terminals and different techniques for managing such communication. Different PSPs, of course, may choose different PCS technologies for many reasons.
A PCS network can be viewed as comprised of two major components: network infrastructure and access infrastructure. Network infrastructure contains the switching resources, and in some cases it may include the mobility management databases such as Home Location Register (HLR) and Visitor Location Register (VLR). Access infrastructure contains the access systems, which are referred to herein as Radio Ports (RPs), access system controllers referred to as Radio Port Control Units (RPCUs), and where used, Radio Access Service Controllers, referred to herein as Access Managers (AMs).
When a PSP decides to use an LEC's network infrastructure for switching, this is attractive to the LEC, because it maximizes the use of the LEC network by the PSP, and therefore maximizes the revenue that the LEC can earn from the PSP. It is also attractive to the PSP, because it minimizes the capital investment it will need to put functioning PCS networks into operation.
Interworking between a PSP and an LECs defines an interface having two components: namely, an integrated services digital network (ISDN) programmed component, which supports call processing operations (call setup and termination) and hand over operations (maintaining calls as the mobile terminal moves from one serving area to another); and an IS-41+ programmed component, sometimes referred to as "Generic C Mobility Management" which supports connection and disconnection of the mobile terminals from the network, including operations required for registration, deregistration, authentication of mobile terminals and control of encryption keys for secure communications with the mobile terminals. These interfaces of the PCS network must have access management (AM) functionality which converts various protocols used by access system controllers (BSC) to the standard IS-41+ protocol for communication with the LEC networks. The BSCs when used in a network having a target-centric handover, are referred to herein as Radio Port Control Units (RPCUs), and the AM is referred to as a Radio Access Service Controller (RASC) for such networks to correspond to a major suppliers terminology.
When a mobile terminal moves from the geographic region served by one access system to the geographic region served by another access system, any call in progress to that mobile terminal must be switched from the assigned radio channel on the one access system to a newly assigned channel on the other access system. This operation is known as handover, and requires appropriate operations by both the PCS network and the switching centers of the LEC network.
Automatic Link Transfer (ALT) is a new capability defined for the ISDN interface to enable hand over between access systems. This capability supports a "target-centric" handover procedure--i.e. a handover procedure in which a access system or access system controller which is not currently serving a mobile terminal identifies that it is capable of serving that mobile terminal and initiates a handover operation. For example, in a target-centric handover, the access system measures signals from terminals it is not serving, and, if any of those signals exceed a threshold indicating that the access system could communicate more effectively with the terminal sending that signal, the target access system initiates a handover procedure to switch the terminal to one of its free channels. In this example, the PCS network detects the handover condition and initiates handover, thus it may be referred to as a "network-centric" "target-centric" handover.
In another type of target-centric handover, the mobile terminal initiates the handover. For example, the terminal measures signals from potential target access systems which are not serving it, and, if any of those signals exceed the signals it is receiving from the access system currently serving it, it initiates a handover. This would be a "terminal-centric" "target-centric" handover.
Other PCS technologies use a "source-centric" handover technique. For example, the serving access system measures signals from terminals it is serving, and, if any of these signals fall below a threshold, the serving or source access system initiates handover from the terminal sending that signal. This approach may be termed "network-centric" "source-centric." Also, the mobile terminal may measure the signal from the access system currently serving it, and, if that signal falls below a threshold, it initiates handover to another access system. This approach is termed "terminal-centric" "source-centric."
A PCS access technology which uses the target-centric hand over works well with PCS networks which also employ target-centric hand over. However, it is conceivable that a PCS access technology that uses source-centric hand over might be required to work with an LEC network employing target-centric hand over.
In light of the foregoing, there is a need for a method and system that is capable of effectively supporting source-centric PCS hand over when the network infrastructure only supports target-centric hand over.